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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Tue, 1 Oct 2019 12:37:01 +0100 Received: from d06av25.portsmouth.uk.ibm.com (d06av25.portsmouth.uk.ibm.com [9.149.105.61]) by b06cxnps3074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x91Bb0Qe57082092 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 1 Oct 2019 11:37:00 GMT Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 0FFCA11C054; Tue, 1 Oct 2019 11:37:00 +0000 (GMT) Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 6CFE711C04A; Tue, 1 Oct 2019 11:36:57 +0000 (GMT) Received: from linux.vnet.ibm.com (unknown [9.122.211.122]) by d06av25.portsmouth.uk.ibm.com (Postfix) with SMTP; Tue, 1 Oct 2019 11:36:57 +0000 (GMT) Date: Tue, 1 Oct 2019 17:06:56 +0530 From: Srikar Dronamraju To: Peter Zijlstra Cc: Qian Cai , akpm@linux-foundation.org, bigeasy@linutronix.de, tglx@linutronix.de, thgarnie@google.com, tytso@mit.edu, cl@linux.com, penberg@kernel.org, rientjes@google.com, mingo@redhat.com, will@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, keescook@chromium.org Subject: Re: [PATCH] sched: Avoid spurious lock dependencies Reply-To: Srikar Dronamraju References: <1568392064-3052-1-git-send-email-cai@lca.pw> <20190925093153.GC4553@hirez.programming.kicks-ass.net> <1569424727.5576.221.camel@lca.pw> <20190925164527.GG4553@hirez.programming.kicks-ass.net> <1569500974.5576.234.camel@lca.pw> <20191001091837.GK4536@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20191001091837.GK4536@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.9.4 (2018-02-28) X-TM-AS-GCONF: 00 x-cbid: 19100111-0008-0000-0000-0000031CBD92 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19100111-0009-0000-0000-00004A3B677A Message-Id: <20191001113513.GB32306@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-10-01_06:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=27 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1908290000 definitions=main-1910010106 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: > Subject: sched: Avoid spurious lock dependencies > > While seemingly harmless, __sched_fork() does hrtimer_init(), which, > when DEBUG_OBJETS, can end up doing allocations. > NIT: s/DEBUG_OBJETS/DEBUG_OBJECTS > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 7880f4f64d0e..1832fc0fbec5 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -6039,10 +6039,11 @@ void init_idle(struct task_struct *idle, int cpu) > struct rq *rq = cpu_rq(cpu); > unsigned long flags; > > + __sched_fork(0, idle); > + > raw_spin_lock_irqsave(&idle->pi_lock, flags); > raw_spin_lock(&rq->lock); > > - __sched_fork(0, idle); > idle->state = TASK_RUNNING; > idle->se.exec_start = sched_clock(); > idle->flags |= PF_IDLE; > Given that there is a comment just after this which says "init_task() gets called multiple times on a task", should we add a check if rq->idle is present and bail out? if (rq->idle) { raw_spin_unlock(&rq->lock); raw_spin_unlock_irqrestore(&idle->pi_lock, flags); return; } Also can we also move the above 3 statements before the lock? -- Thanks and Regards Srikar Dronamraju